ELASTIC-ANISOTROPY OF SHORT-FIBER REINFORCED COMPOSITES

Short-fibre reinforced composites are attractive because of their ease of fabrication and relatively low cost. They consist of partially aligned short fibres in a continuous matrix material, the orientation of the fibres depending on the processing conditions employed. In this report a theoretical treatment of the elastic anisotropy of a short-fibre reinforced composite resulting from a partial orientation of the fibres is presented. The elastic stiffnesses of the composite may be calculated in terms of the coefficients W(lmn) in an expansion of the fibre-orientation distribution function in generalized Legendre functions. Since the elastic stiffness tensor is of fourth rank, it depends only on the coefficients W(lmn) for l less-than-or-equal-to 4. These coefficients may be determined from the angular variation of the ultrasonic velocity. This allows the fibre-orientation distribution to be plotted. Since the anisotropy in strength properties originates from the preferred orientation of fibres, the prediction of the fibre orientation distribution function will have an important application in the failure analysis of these materials.